Clad aluminum alloy metals are joined by a brazing process using a metal filler wherein the metals are heated to near eutectic temperature where the metals bond to form a joint. Controlled atmospheric brazing of aluminum heat exchangers is practiced in automobile manufacturing. In heat exchangers, the braze alloy typically consists of a 4000 series aluminum alloy clad layer roll bonded to a 3000 series aluminum core alloy that is stamped into individual components, assembled into the heat exchanger, fluxed, and brazed in a continuous atmospheric braze furnace using nitrogen as a cover gas to prevent oxidation.
The application of a potassium fluoro-aluminate flux to reduce the native oxide layer on the aluminum alloy is a critical step in achieving a sound, high quality braze joint. Braze sheet material containing high levels of magnesium greater than 0.25 percent by weight cannot be brazed using potassium fluoro-aluminate flux, and more aggressive chloride based fluxes must be used. Unfortunately, more aggressive chloride based fluxes are highly corrosive to the aluminum components after brazing. It is desirable to use 6000 series aluminum alloy instead of 3000 series because of its greater post braze mechanical strength. However, the presence of 0.9 to 1.2 percent by weight of magnesium in the 6000 series alloy prevents its use because of the reactivity of the magnesium with the fluoride flux resulting in a poor braze joint.
There is a process for depositing a thin electroplated nickel or cobalt alloy coating onto clad braze sheet alloys, such as 4000 series alloy cladding on 3000 series alloy core material, for fluxless inert gas brazing of aluminum heat exchangers. The nickel and cobalt alloy coatings are applied directly onto the clad braze sheet coil in a continuous bath plating operation. In this process, the entire component is coated which makes the manufacturing process relatively expensive. Accordingly, it will be appreciated that it would be highly desirable to economically fabricate an automotive heat exchanger or other component using 6000 series aluminum alloys without using flux.